Digital prefiltering of encoded video signals

Abstract

Digital prefiltering of luminance and chrominance components for an encoded video signal is performed to prevent cross color and dot crawl errors when the encoded video signal is decoded. The luminance component is filtered using a two- or three-dimensional chrominance bandpass filter to generate luminance correction limiting values corresponding to cross color errors that would occur when a conventionally encoded video signal is decoded. The luminance component also is filtered individually in each dimension, horizontally, vertically and/or temporally, to obtain luminance dimensional correction values. From the luminance correction limiting values and corresponding luminance dimensional correction values, luminance correction values are obtained by a two step decision process. The luminance correction values are added to the luminance component to provide the prefiltered luminance component. In like manner chrominance correction limiting values and chrominance dimensional correction values are generated and used to obtain chrominance correction values that are added to the chrominance component to provide the prefiltered chrominance component. The prefiltered components are combined, along with synchronizing signals, to produce the encoded video signal.

What is claimed is: 
     
       1. A method of encoding a luminance and two chrominance components representing a color video image into an encoded video signal comprising the steps of: filtering the luminance component in multiple dimensions to produce a luminance limit signal that represents peaks and edges in the luminance component and to produce a luminance correction signal in each dimension;   correcting the luminance component as a function of the luminance limit signal and the luminance correction signals only where the peaks and edges occur to produce a prefiltered luminance component that compensates for cross color errors when the encoded video signal is decoded;   filtering each chrominance component in multiple dimensions to produce prefiltered chrominance components that compensate for peaks and edges in the chrominance components which produce dot crawl errors when the encoded video signal is decoded and that are the same as the corresponding chrominance components except where the edges occur; and   combining the prefiltered luminance and chrominance components with appropriate synchronizing signals to produce the encoded video signal.   
     
     
       2. A method as recited in claim 1 wherein the luminance component filtering step comprises the steps of: chrominance bandpass filtering the luminance component in multiple dimensions to produce the luminance limit signal; and   lowpass filtering the luminance component in each dimension to produce the luminance correction signals.   
     
     
       3. A method as recited in claim 1 wherein the chrominance component filtering step comprises the steps of: filtering each chrominance component to produce respective chrominance correction signals; and   adding the chrominance correction signals to the corresponding chrominance components to produce the prefiltered chrominance components.   
     
     
       4. A method as recited in claim 1 wherein the chrominance component filtering step comprises the steps of: filtering each chrominance component in multiple dimensions to produce respective chrominance color correction signals having values that represent the peaks and edges in each chrominance component; and   adding the chrominance color correction signals to the corresponding chrominance components to produce the prefiltered chrominance components.   
     
     
       5. A method as recited in claim 1 wherein the correcting step comprises the steps of: determining from the luminance correction signals and the luminance limit signal a final luminance correction signal; and   adding the final luminance correction signal to the luminance component to produce the prefiltered luminance component.   
     
     
       6. A method as recited in claim 1 wherein the chrominance components filtering step comprises the steps of: filtering each chrominance component in each dimension to produce respective chrominance limit signals having values representing the peaks and edges in each chrominance component and to produce respective chrominance correction signals in each dimension for each chrominance component; and   correcting the corresponding chrominance components as a function of the respective chrominance limit signals and the chrominance correction signals to produce the prefiltered chrominance components.   
     
     
       7. A method as recited in claim 6 wherein the chrominance components correcting step comprises the steps of: determining from the chrominance correction signals and the chrominance limit signal respective final chrominance correction signals for each chrominance component; and   adding the final chrominance correction signals to the corresponding chrominance components to produce the prefiltered chrominance components.   
     
     
       8. An apparatus for encoding a luminance and two chrominance components representing a color video image into an encoded video signal comprising: means for filtering the luminance component in multiple dimensions to produce a luminance limit signal that represents peaks and edges in the luminance component and to produce a luminance correction signal in each dimension;   means for correcting the luminance component as a function of the luminance limit signal and the luminance correction signals only where the peaks and edges occur to produce a prefiltered luminance component that compensates for cross color errors when the encoded video signal is decoded;   means for filtering each chrominance component in multiple dimensions to produce prefiltered chrominance components that compensate for peaks and edges in the chrominance components which produce dot crawl errors when the encoded video signal is decoded and that are the same as the corresponding chrominance components except where the edges occur; and   means for combining the prefiltered luminance and chrominance components with appropriate synchronizing signals to produce the encoded video signal.   
     
     
       9. An apparatus as recited in claim 8 wherein the chrominance component filtering means comprises: means for filtering each chrominance component to produce respective chrominance correction signals; and   means for adding the chrominance correction signals to the corresponding chrominance components to produce the prefiltered chrominance components.   
     
     
       10. An apparatus as recited in claim 8 wherein the chrominance component filtering means comprises: means for filtering each chrominance component in multiple dimensions to produce respective chrominance color correction signals having values that represent the peaks and edges in each chrominance component; and   means for adding the chrominance color correction signals to the corresponding chrominance components to produce the prefiltered chrominance components.   
     
     
       11. An apparatus as recited in claim 8 wherein the luminance component filtering means comprises: means for chrominance bandpass filtering the luminance component in multiple dimensions to produce the luminance limit signal; and   means for lowpass filtering the luminance component in each dimension to produce the luminance correction signals.   
     
     
       12. An apparatus as recited in claim 8 wherein the correcting means comprises: means for determining from the luminance correction signals and the luminance limit signal a final luminance correction signal; and   means for adding the final luminance correction signal to the luminance component to produce the prefiltered luminance component.   
     
     
       13. An apparatus as recited in claim 8 wherein the chrominance components filtering means comprises: means for filtering each chrominance component in each dimension to produce respective chrominance limit signals having values representing the peaks and edges in each chrominance component and to produce respective chrominance correction signals in each dimension for each chrominance component; and   means for correcting the corresponding chrominance components as a function of the respective chrominance limit signals and the chrominance correction signals to produce the prefiltered chrominance components.   
     
     
       14. A method as recited in claim 13 wherein the chrominance components correcting means comprises: means for determining from the chrominance correction signals and the chrominance limit signal respective final chrominance correction signals for each chrominance component; and   means for adding the final chrominance correction signals to the corresponding chrominance components to produce the prefiltered chrominance components.